The present invention relates generally to power conversion systems. More particularly, the invention relates to a power conversion system used in a rotary power generation system for converting a variable-frequency alternating current produced by a variable-speed rotary power generator into an alternating current with controlled amplitude or frequency for feeding an electric grid.
One type of power generation system comprises a rotary power generator for generating an alternating current with a variable frequency by rotation of a generator rotor and a power conversion system for converting the variable-frequency alternating current into an alternating current with controlled amplitude or frequency to be supplied to an electric grid. One example of such a power generation system comprises a variable-speed wind turbine power generation system.
Variable-speed wind turbine power generation systems include generators with rotation speeds that vary with wind speed and generate an alternating current with a variable frequency. Variable speed wind turbine generators can provide more energy over a range of wind speeds as compared with wind turbine generators requiring a constant speed of operation.
Power conversion systems for variable-speed wind turbines typically include a generator side power electronic converter (“generator side converter”) for converting the variable-frequency alternating current into a direct current at a DC link and a line (or grid) side power electronic converter (“line side converter”) for converting the direct current at the DC link into an alternating current with controlled amplitude or frequency for feeding the grid. It is desirable to transmit as much of the wind power to the grid as possible while protecting the power generation system under different wind and grid conditions.